Some printing mechanisms such as Inkjet printers include sensors that facilitate pen alignment, media type detection, media edge detection, and/or other functions. Unfortunately, many prior sensors—particularly, sensors that have high margins for aerosol, paper dust, ambient light and page life—are too costly to be incorporated into the low cost printing mechanisms demanded by consumers today. The high price of such sensors effectively forecloses their inclusion in printing mechanisms which themselves have virtually become consumables. It would be desirable to be able to provide a low cost optical sensor suitable for such printing mechanisms.